1. Technical Field
The present disclosure relates to a rotating refiner plate with a pattern of bars and grooves creating a continuous transition zone spanning from an area near the inner portion of the plate or plate segment (or sector) near the breaker bar zone, to an area near the periphery of the plate or plate segment (or sector).
2. Related Art
Conventional refiner plates generally comprise a substantially annular inner zone characterized by very coarse bars and grooves where feed material is reduced in size and given a radial (from the axis of rotation of the refiner plate toward the periphery) component of movement without substantial refining action. This is called the breaker bar zone. A second, annular outer zone receives the material from the first zone and performs a relatively coarse refining action at its inner portion followed by a higher degree of refining at its outer portion. This outer zone is known as the refining zone.
The refining zones of conventional refiner plates typically have one or more distinct substantially annular refining regions, each having its own bar and grove configuration, with the density of the bar pattern getting higher as one moves from the innermost zone (feeding area) to the outermost zone (exit area). Between each refining region is a transition zone. Transition zones commonly appear to be generally circular or annular or spread over a relatively short distance in an arc relative to the axis of rotation. Transition zones can also incorporate various shapes and configurations, such as the “Z shape” disclosed in U.S. Pat. No. 5,383,617, a “V shape,” or “W shape.” Even when a transition zone is spread over a certain area, conventional refiner plate designs typically have very separate refining regions with relatively constant bar and groove designs and somewhat restrictive transition zones in between the separate refining regions. Though refiner plates may or may not be segmented, they are usually formed by attaching a plurality of segments or sectors side-by-side (laterally), or in an annular array onto the disc surface, with the zone transitions often being symmetric on either side of a radially extending central axis on each segment or sector.
Refiner plates have been in use for many years to separate wood into individual fibers, as well as to develop these fibers into suitable paper-making or board-making fibers. The process is highly energy-demanding and there have long been attempts at reducing the energy requirement for refining wood into suitable paper-making fiber. Most successful attempts at reducing energy consumption have resulted in an unacceptable drop in the properties and quality of the produced fiber.
Laboratory experiments using a combination of force and temperature sensors have been made with a variety of refiner plate models. It has been found that the most significant detrimental contributor to both energy consumption and fiber quality is a pattern on a refiner plate that leads to a radially uneven fiber pad distribution. This means that the pad of fiber is of uneven thickness on the surface of the refiner plate, especially moving in a radial direction from the inner edge to the outer edge. In other words, undesirable patterns for achieving optimal energy consumption and fiber quality are those which result in a larger accumulation of fiber on a given radial location. Larger radial accumulations are typically associated with points where a bar and groove pattern is changing, typically from a coarser inlet pattern to a finer pattern toward the periphery, or sometimes with a poor radial distribution of dams that restricts flow in the grooves.
To optimize refining performance, full utilization of a plate's refining surface is needed. This requires a gradual reduction in bar and groove widths from the feeding area (usually the inner area) to the exit area. Such a configuration makes the refiner plate better-suited to the combination of the natural feeding behavior of the refiner (more retention in the feeding area) and the gradual reduction in particle size going from wood chips, to fiber bundles, and then to individual fibers.
Typical bar and groove geometries used in refiner plate patterns, namely the transition zones, create areas where feed stock stalls and a large fiber accumulation results. In addition, large fiber accumulation in one area leads to over-refining and unwanted fiber cutting. Areas between the over-refined areas are used with less efficiency, because the low or inadequate amount of fiber accumulation does not facilitate the correct application of energy intensity.
Early attempts to remove fiber buildups caused by the configuration of the transition zones were made by incorporating designs with bars and grooves that converge toward the periphery of the refining zone. These converging bar and groove designs, however, tend to plug easily as feed material is forced in converging channels. These designs also tend to produce patterns with a wider span of pumping and holding bar angles relative to a line extending laterally across a refiner plate segment or sector, producing a less homogeneous fill rate across the refiner plate surface, as well as uneven refining due to some of the material having longer and shorter retention times in the refining zone.
Accordingly, there is a need for an improved refiner plate design with no specific radial transition point between refining zones in order to eliminate radial build-ups of fiber while achieving good operation and producing good and even quality fiber at low energy levels. There is an additional need for an improved refiner plate design with a bar and groove pattern that becomes gradually finer from the axis of rotation to the periphery of the plate to further aid in the elimination of buildups of fiber with minimal negative effects on operation and fiber quality. There is yet another need for restrictions in the refiner plate design, such as with dams, which should be distributed evenly in the radial direction in order to further minimize buildups of fiber without negative effects. It is to these needs and others that the present invention is directed.